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Posted 8 Jan 2001

Bridge Pattern - Bridging the gap between Interface and Implementation

, 8 Jan 2001
This article discusses the Bridge Pattern, what it is, why and when it is needed.
// BridgeDoc.cpp : implementation of the CBridgeDoc class
//

#include "stdafx.h"
#include "Bridge.h"

#include "BridgeDoc.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif

/////////////////////////////////////////////////////////////////////////////
// CBridgeDoc

IMPLEMENT_DYNCREATE(CBridgeDoc, CDocument)

BEGIN_MESSAGE_MAP(CBridgeDoc, CDocument)
	//{{AFX_MSG_MAP(CBridgeDoc)
	ON_COMMAND(ID_FILE_OPEN, OnFileOpen)
	//}}AFX_MSG_MAP
END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////////
// CBridgeDoc construction/destruction

CBridgeDoc::CBridgeDoc()
{
	// Step 1 - Initialize class members
	m_pImage = NULL;
}

CBridgeDoc::~CBridgeDoc()
{
	// Step 1 - Delete image object, if it is valid
	if( m_pImage != NULL )
	{
		delete m_pImage;
	}
}

/////////////////////////////////////////////////////////////////////////////
// CBridgeDoc diagnostics

#ifdef _DEBUG
void CBridgeDoc::AssertValid() const
{
	CDocument::AssertValid();
}

void CBridgeDoc::Dump(CDumpContext& dc) const
{
	CDocument::Dump(dc);
}
#endif //_DEBUG

/////////////////////////////////////////////////////////////////////////////
// CBridgeDoc commands

void CBridgeDoc::OnFileOpen() 
{
   CFileDialog FileDialog( TRUE, NULL, NULL,
                        OFN_HIDEREADONLY | OFN_OVERWRITEPROMPT 
                        | OFN_PATHMUSTEXIST | OFN_FILEMUSTEXIST, 
                        "Bitmap Files (*.bmp;*.wmf)|*.bmp;*.wmf|DIB Files (*.dib)|*.dib|All Files (*.*)|*.*|||", 
								NULL );

	// Step 1 - Show the dialog box and open the document, if a valid file name is selected
	if( FileDialog.DoModal() == IDOK )
	{
		OnOpenDocument( FileDialog.GetPathName() );
	}
}

BOOL CBridgeDoc::OnOpenDocument( LPCTSTR lpszPathName ) 
{
	CWaitCursor WaitCursor;
	CImage		* pTempImage = NULL;

	// Step 1 - Create an image object
	pTempImage = new CBmpImage;
	if( pTempImage == NULL )
	{
		CHAR szTempString[ 512 ];

		memset( szTempString, 0, sizeof( szTempString ) );
		sprintf( szTempString, "Insufficient memory.\n");
		AfxMessageBox( "Insufficient memory", MB_ICONSTOP | MB_OK );
		return FALSE;
	}

	// Step 2 - Load image file and configure with the runtime information 
	// of the implementation class, CWinImp in this case
	if( pTempImage->Load( lpszPathName, RUNTIME_CLASS( CWinImp ) ) != SUCCESS )
	{
		// Step 3 - Delete object and display error message
		delete pTempImage;
		CHAR szTempString[ 512 ];

		memset( szTempString, 0, sizeof( szTempString ) );
		sprintf( szTempString, "Unable to open the image file %s.\n", lpszPathName );
		AfxMessageBox( szTempString, MB_ICONINFORMATION | MB_OK );
		return FALSE;
	}

	// Step 4 - Delete old image object, if it is valid
	if( m_pImage != NULL )
	{
		delete m_pImage;
	}
	// Step 5 - Assign, new image object
	m_pImage = pTempImage;
	UpdateAllViews( NULL );
	SetPathName( lpszPathName );
	return TRUE;
}

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About the Author

T. Kulathu Sarma
Switzerland Switzerland
Kulathu Sarma is working as a Technology Manager for GoldAvenue, a company based in Geneva, Switzerland and responsible for supporting e-business initiatives of GoldAvenue in B2B and B2C Sectors. He has been programming in C/C++ for 9 years and actively working on Patterns for the past 5 years.

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